Thirteen-year-old Sara Lockwood thinks she will never get over the loss of Pepper, her pony who was recently killed in a hit-and-run accident - the driver having never been caught. She feels angry and lonely, but worst of all, she feels cut off from all her friends at the Pony Club as she no longer has a pony to ride and groom. But things take an unexpected turn as a cruelly neglected bay mare, Polly, comes into her life, desperately in need of someone to look after and love her - could Sara be that someone?With a lot of hard work and help from her family and friends, Sara nurses Polly back to health, and in turn Polly helps Sara come to terms with losing Pepper; but can she help solve a mystery that has troubled Sara since the accident?